Damped electric circuit board



p 15, 1964 R. P. THORN 3,149,265

DAMPED ELECTRIC CIRCUIT BOARD Filed Feb. 21, 1962 United States Patent M3,149,265 DAMPED ELECTRIC CIRCUIT BOARD Richard P. Thorn, Erie, Pa.,assignor to Lord Manufacturing Company, Erie, Pa., a corporation ofPennsylvania Filed Feb. 21, 1962, Ser. No. 174,875 Claims. .(Cl.,317100)This invention is a circuit enclosure intended to protect electriccircuit components from high frequency vibrations. Instead of mountingthe components on the board, the components are placed in pre-moldedcavities in a laminate of structural plates and viscoelastic dampingmaterial.

In the drawing, FIG. 1 is a fragmentary section through a board showinga tubular component connected on one side of the board to printed wiringand on the opposite side of the board to welded wires, FIG. 2 is asimilar section showing a transistor received in a metal shell or socketfor dissipating the heat, and FIG. 3 is a perspective illustratingpossible arrangements of the component receiving cavities.

The enclosure has a plurality of plates or layers 1 and 2 of structuralmaterial such as aluminum, fiberglass reinforced plastic, etc. withadjacent layers bonded to an intermediate layer 3 of viscoelasticmaterial having high damping or internal friction and a modulus ofelasticity low compared to the structural material. Viscoelasticmaterials are well known under chemical and proprietary names and thechoice for any particular environment is a matter of engineering. Thethickness of the layers 1, 2 and 3 is a matter of calculation for theload to be carried, the frequencies encountered and the dampingdesired.Thicknesses varying from .005 inch to inch have been used and this rangeis by way of example and not by way of limitation. The number of layersmaking up the basic enclosure may be increased if desired.

On the upper surface of the enclosure is an outer skin of insulatingmaterial 4 which is bonded to a viscoelastic layer 5 in turn bonded tothe upper surface of the layer 1. The skin 4 carries a printed wiringpattern 6. On the lower surface of the enclosure is a grid of weldedwiring 7 resting on a layer 8 of viscoelastic material bonded to theouter or under surface of the structural plate 2. At suitable locationsin the enclosure are cavities or sockets 9 having an inside diameter inthe as molded condition slightly smaller than the outside diameter of acomponent 10. When the enclosure is molded in one operation as shown,the cavities or sockets 9 extend through the outer skin 4 to permitinsertion of the components. In the alternative, the skin 4 may be aseparately manufactured printed wiring board added to the enclosureafter the insertion of the components, in which case the openings in theskin 4 need only be large enough to receive the component leads. In factit might be easier to solder the leads to the printed wiring if theopenings in the skin 4 were only slightly larger than the componentleads. The diameter of the cavity 9 is substantially less than thediameter of registering holes 11 in the structural plates 1 and 2 sothat there is formed a skin 12 of viscoelastic material between theedges of the holes 11 and the bore of the cavity 9 which provides afriction grip on the inserted component and also provides a dampingconnection to the component which protects it from high frequencyvibration. At the upper end the component lead 13 is connected to theprinted wiring. At the lower end the component lead 14 is connected tothe metal grid wiring. It will be understood that either form of wiringmay be used on both sides or that wiring may be used on only one side.

In the enclosure shown in FIG. 2, there are metal plates 15 and 16between which is sandwiched a layer 17 3,149,265 Patented Sept. 15, 1964of viscoelastic material. A skin 18 of insulating material carryingprinted wiring 19 is bonded to the upper side of the plate 15by aviscoelastic layer 20. Bonding is not necessary. A viscoelastic layer 21is bonded to the side of the plate 16. Prior to the molding operationduring which all of the layers are bonded together, a metal shell 22 isinserted into registering openings 23 in good thermal conductiverelation to the metal plates 15 and 16. The purpose of this shell is toprovide a heat sink for a transistor 24 or other component insertedwithin the shell. During the molding operation, the viscoelastic layers17, 20 and 21 are bonded to the outer surface of the shell and some ofthe elastomer flows between the shell and the openings 23 in the metalplates 15 and 16. The shell accordingly does not interfere with thedamping. If desired, the inner surface of the shell 22 may have acoating of the elastomer to provide a grip on the component 24. The heatsink provided by the shell 22 in association with the metal plates 16conducts heat away from the component which could interfere with itsoperation.

In FIG. 3 there is shown a circuit enclosure having three layers 24, 25,26 of structural material and four layers 27, 28, 29, 30 of viscoelasticmaterial. These are bonded together to form a damped laminate. In eachof the layers there is one or more holes which are arranged in registerwith each other prior to molding. The shape of these holes is a matterof design and may be round, hexagonal or oval as illustrated, or of anyother suitable design adapted to receive the components.

What is claimed as new is:

1. A circuit enclosure comprising a plurality of sheets of structuralmaterial with adjacent sheets bonded to opposite sides of an interveninglayer of viscoelastic material of high internal friction and low modulusof elasticity compared to the structural material, said structuralsheets and the intermediate viscoelastic layer having registeringopenings therein, a tubular lining of viscoelastic material extendingthrough and bonded to the edges of said openings and providing acomponent receiving socket.

2. A circuit enclosure comprising a plurality of sheets of metal withadjacent sheets bonded to opposite sides of an intervening layer ofviscoelastic material of high internal friction and low modulus ofelasticity compared to the metal, coatings of viscoelastic materialbonded to the outermost surface of said sheets, said sheets and theviscoelastic layer registering openings therein, a metal sleeveextending through said openings in good thermal conducting relation tothe sheets and bonded to the viscoelastic layers, the metal sleeveproviding a component receiving socket and serving as a heat sink.

3. A circuit enclosure comprising a plurality of sheets of structuralmaterial with adjacent sheets bonded to opposite sides of an interveninglayer of viscoelastic material of high internal friction and low modulusof elas ticity compared to the structural material, coatings ofviscoelastic material bonded to the outermost surfaces of said sheets,said structural sheets and the viscoelastic layers having registeringopenings therein, a tubular lining of viscoelastic material extendingthrough and bonded to the edges of said openings and providing acomponent receiving socket, and wiring on at least one of the coatingsof viscoelastic material.

4. A circuit enclosure comprising a plurality of sheets of structuralmaterial with adjacent sheets bonded to opposite sides of an interveninglayer of viscoelastic material of high internal friction and low modulusof elasticity compared to the structural material, said structuralsheets and the intermediate viscoelastic layer having registeringopenings therein, a tubular lining of viscoelastic material extendingthrough and bonded to the edges of said openings and providing acomponent receiving socket, a sheet of insulating material bonded to theouter surface of one of said structural sheets by a layer ofviscoelastic material and having an opening registering with saidsocket, and printed wiring carried on the outer surface of said sheet ofinsulating material.

5. A circuit enclosure comprising a plurality of sheets of metal withadjacent sheets bonded to opposite sides of an intervening layer ofviscoelastic material of high internal friction and low modulus ofelasticity compared to the metal, coatings of viscoelastic materialbonded to the outermost surfaces of said sheets, said sheets and theviscoelastic layers registering openings therein, a metal i sleeveextending through said openings in good thermal conducting relation tothe sheets and bonded to the viscoelastic layers, the metal sleeveproviding a component receiving socket and serving as a heat sink, asheet of insulating material bonded to the outer surface of one of saidviscoelastic coatings, and printed Wiring carried a on the outer surfaceof said sheet of insulating material.

References Qited in the file of this patent UNITED STATES PATENTS

1. A CIRCUIT COMPRISING A PLURALITY OF SHEETS OF STRUCTURAL MATERIALWITH ADJACENT SHEETS BONDED TO OPPOSITE SIDES OF AN INTERVENING LAYER OFVISCOELASTIC MATERIAL OF HGH INTERNAL FRICTION AND LOW MODULUS OFELASTICITY COMPARED TO THE STRUCTURAL MATERIAL, SAID STRUCTURAL SHEETSAND THE INTERMEDIATE VISCOELASTIC LAYER HAVING REGISTERING OPENINGSTHEREIN, A TUBULAR LINING OF VISCOELASTIC MATERIAL EXTENDING THROUGH ANDBONDED TO THE